The invention relates to a railway track structure formed of at least a pair of rails, which are fastened to sleepers via which they are supported on a bed of ballast material.
This invention also relates to a method of making track structures and a new ballast bed for such track structures.
Railway track structures of the type indicated above are generally known. Although these known railway track structures are found to be quite satisfactory, their proper functioning is not quite so easy to keep up.
Continuous movement of traffic causes both disturbances to the packing of the ballast underneath the sleepers and pulverization of the ballast. Particularly a conventional railway track with a ballast bed entirely formed of broken stone or pebbles requires a great deal of maintenance. Especially the practically cohesionless supporting layer rapidly pulverizes to a greater or lesser extent under the influence of the dynamic load of the traffic plying thereon.
Further, the transport capacity of existing or newly laid railway tracks is often required to be increased, which can be realized with heavier and more frequent trains per day that generally attain higher speeds. This increase in transport capacity leads to higher and heavier loads being applied to the railway track in its entirety and to its individual components, an important role being played by the dynamic load of the trains that ply on the rails.
In the case of heavy traffic schedules conventional track maintenance is no longer possible during the day, so that the work must be done at night. The maintenance work is done manually or with the help of machines. Operation of the heavy duty ballast tampers and ballast consolidating machines is very slow and is attended with a high noise level.
Moreover, on railway track sections, which frequently carry bulk material, or in deserts and other loose soil dry areas the ballast bed material, becomes fouled up with this bulk material or sand, which also detracts from the proper functioning of the ballast bed.
As far as the maintenance of these conventionally built railway track structures is concerned, the high demands made on it these days can be met only with great difficulty and generally at prohibitively high cost.
Two separate systems exist as devices for securing railroad rails. On the one hand, the attachments for sleepers or supports on a ballast foundation, and on the other hand the superstructure for a solid track, i.e. securing rails for a superstructure without ballast.
The invention has for its object to provide an improved railway track, which does not have the limitations of the prior art railway tracks and no longer has the afore-mentioned disadvantages.
According to this invention there is provided track structure for fastening rails comprising
[i] a ballast bed consisting of a plurality of discrete gabion type inter fitting elements;
[ii] sleepers for fixing rails thereto adapted to be laid and fitted on the said ballast bed;
[iii] resiliently compressible pads adapted to be provided between the said sleepers and the ballast bed.
Typically, the elements of the ballast bed are defined by support box type elements in which ballast material such as pebbles and broken stones is filled.
Typically, the support elements are in the form of wire boxes or in the form of a box having perforated walls.
In accordance with a preferred embodiment of the invention the walls of the support element are tensioned and the ballast material filled in the support elements include resiliently compressible elements such as rubber tyre crumbs.
Typically, the resilient pad is provided between the sleeper and the ballast bed is an elastomeric sheet element reinforced on the inside or the outside, preferably provided on the surface of the gabions forming the ballast bed or within the gabions forming the ballast bed.
In accordance with one embodiment of the invention the support element for the gabions forming the ballast bed has a wall which constitutes the resilient element.
The invention also discloses a method of making a track structure consisting the steps of
preparing a sub soil bed for forming the track structure thereon;
filling ballast material in support elements to form ballast gabions;
interfitting the ballast gabions to form a ballast bed over the subsoil bed;
providing resilient elements over distinct sleeper mounting locations on the formed ballast bed; and
fitting sleepers over the resilient elements.
According to another aspect of this invention there is provided a ballast bed for the track structure consisting of inter fitting gabions formed by filling support elements with ballast material at least some of the gabions provided with resilient elements for mounting sleepers thereon.
Typically the ballast bed has ballast material, which includes crumbs of resilient material, and the support elements are in the nature of a wire box and the resilient element is a wall of the support element.
In accordance with another embodiment the resilient element is provided either outside or inside the gabion.
According to the invention therefore the railway track structure is characterized in that beneath the sleepers the ballast is confined in wire boxes known as gabions.
In accordance with a preferred embodiment of the invention, the ballast is provided in one or more supporting elements in which the ballast material is filled.
In accordance with another aspect of the invention, it relates to a device for securing railway rails on a ballast track or a solid track in a highly resilient manner.
Ballast tracks, which are fitted with the standard superstructure also frequently, exhibit rail compression values that are too low for use in high-speed transport on new routes. The resilience of ballast permits track compression which results in a rail head depression of about 0.6 mm. This track compression is clearly below today""s desired rail head depression of 1.5 mm.
This invention envisages the use of at least one resilient layer between the sleeper and the ballast track in order that the track system is self stabilizing.
The use of the resilient intermediate layer, typically in the form of a rubber pad, preferably reinforced can achieve a static spring rates of at least c=50-70 kN/mm, which will improve track compression to a rail head depression of above 1.0 mm (in conjunction with the ballast track).
To achieve good track compression and stabilization, a resilient intermediate pad is disposed between the rail sleeper and the ballast bed; this pad ensures sufficient compression.
In accordance with a preferred embodiment of the invention the resilient intermediate pad is reinforced therewithin or on the outside.
Thus the present invention is based on the object of using standard elements and standard sleepers to design a rail attachment, by means of which high rail compression values and proper self stabilization can be achieved.
The device for securing railway rails on a ballast track or a solid track includes a standard sleeper used on the ballast track; consisting of a plurality of gabions holding ballast and a resilient pad placed below the sleeper typically below the rail seat between the sleeper and the gabions.
In accordance with one embodiment of the invention the resilient intermediate pad and/or the gabions may have a larger extension in the sleeper""s longitudinal direction than the rail flange and therefore protrude across the width of the rail flange on both sides. As a result, the pressure is distributed over a larger surface area of the ballast bed via the resilient intermediate pad.
In accordance with another embodiment the resilient pad may be secure with the gabion elements such that the upper wall surface may be flexible/resilient. Alternatively, the rubber resilient pad may be independent of the gabions. The gabions being typically of elements made of wire net or fabric. The resistance of the ballast bed to dynamic load and deformation will be favourably influenced if according to the invention the gabions filled with ballast material are under tension. This tension ensures that the ballast material in the gabion will hold together. The ballast material may be made up of various grades of pebble, crushed stone, pebble-sand mixtures or some other material of sufficient strength. To stabilize elasticity elastic components may be added to the ballast material.
Optionally, the resilient pad may be a bladder of a synthetic polymeric material, which may be placed in the gabion near the closure and inflated with compressed air after tying up the gabion. To this end also use may be made of waste products that are sufficiently elastic.
A simple embodiment of the railway track structure according to the invention is characterized in that beneath each sleeper there are positioned at least two gabions filled with ballast material. The gabions are advantageously so positioned beneath the sleepers that halfway between the two rails the two facing ends of the gabions are spaced at some distance apart. Said space is filled with ballast material or the like.
A particularly effective embodiment according to the invention is characterized in that the sleepers are each positioned within the upper part of a gabion. This provision has the advantage that the gabions need not be fastened to the sleepers.
Also instead of employing a solid wooden sleeper use may with advantage be made of a steel tube having a rectangular cross-section.
Favourable results may in principle also be obtained with the gabions extending beneath the sleepers in longitudinal direction of the rails.
According to the invention the gabions may be filled with some hard ballast material such as pebbles, broken stone, sand and/or slag. Favourable results are also expected if according to the invention the gabions are filled with a mixture of hard ballast material, such as pebbles, broken stone and/or sand, and elastic material, such as pieces of elastomeric material typically waste tyre crumb.
A favourable embodiment of the railway track structure according to the invention is characterized in that measured over their side resting on the subsoil, the filled gabions extending in longitudinal direction of the sleepers have varying lengths and varying transverse dimensions in longitudinal direction of the rails.
It is expected that a railway track structure comprising ballast gabions according to the invention will not require any maintenance for many years as far as the ballast bed is concerned. The gabions are porous and air and water will have access to the contents of the gabions. The filled gabions have a greater width than the sleepers, as a result of which the ballast bed will have a high load bearing capacity and the load is uniformly distributed. The ballast bed according to the invention is also expected to be of satisfactory use in desert-like regions with blowing sand. As a matter of fact, a conventional ballast bed is made impermeable to water by all the sand and loses its elasticity in that fine sand particles will deposit in the ballast bed.
The invention also comprises a method of building a railway track structure by which a bed of ballast material with sleepers and rails is provided, which is characterized according to the invention in that beneath the sleepers there are placed one or more gabions or like containers filled with ballast material. The gabions may with advantage be fastened to the sleepers. A favourable embodiment of the method according to the invention is characterized in that in the gabion filled with ballast material this material is set into vibration in order that it may be compacted before the gabion is closed. It is preferred that the ballast material is set into vibration at a frequency and at an amplitude such that the ballast material behaves practically like a liquid, and the gabion is closed while the ballast material in it is in vibratory motion or afterwards. In that way the filling of the gabions with ballast material will be optimal, with the wire net or fabric material of the filled gabions being tensioned.
When the gabions thus filled are fastened beneath the sleepers, the gabions are somewhat pre-tensioned. Because of this pre-tension the gabions will be more capable of taking up the high dynamic loads applied to the track due to the traffic thereover of trains. A favourable embodiment of the method according to the invention is characterized in that the gabion, after it has successively been filled with ballast material and closed, is so compressed by pre-tension transverse to its longitudinal direction that two opposed flattened faces are formed. For protection, the gabions placed on their supports may be covered with ballast material. In accordance with another embodiment of the invention to achieve a self stabilizing rail track system, at least one compressible resilient pad is positioned between the sleeper and the ballast gabions.
Laying a railway track according to the invention may be simplified by prefabricating a group of sleepers, say 4-6, with gabions filled with ballast material fastened to them and collectively fastening the whole construction to a carrier, such as a mounting rail, after which the carrier with sleepers and gabions is transported to the site for laying the railway track.
The invention also comprises a gabion-shaped body formed by a flexible container filled with ballast material, which body is formed in the manner described hereinbefore for use in the railway track according to the invention.
The invention also comprises a foundation for a railway, a building structure, a machine, a road or some other construction, which is characterized in that said foundation contains a plurality of the afore-described gabion-shaped bodies according to the invention.